Scroll machines derive efficiency and reliability at least in part due to the employment of relatively tight manufacturing tolerances. One way to achieve such tolerances is to use high precision machines and techniques, such as sophisticated (and expensive) numerically controlled machines for machining conventional materials used for scroll machine components. It is thus desirable to use a material that is readily machineable.
One material that popularly has been employed as a scroll machine component material is cast iron. In general, both scroll members of a scroll machine are made from the same material, in order to approximate the same rate of thermal expansion and thereby help reduce the potential for expansion mismatch and associated leakage performance loss. The presence of graphite in at least some cast iron alloys tends to help improve performance by acting as a solid lubricant. The components in turn help form a wear couple for helping to enhance minimizing leakage.
For examples of recent improvements in scroll machine component materials, see, commonly owned U.S. Pat. No. 5,580,401 (Williamson) hereby incorporated by reference.
Though attractive as a relatively high strength to weight material, the use of an aluminum alloy for a scroll machine component material generally has been avoided. Aluminum alloys tend to gall when coupled components wear against each other. In practice, when aluminum alloys have been employed, they have necessitated the undesirable use of sleeve bearings, protective coatings, tip seals, or wear plates between aluminum components.
It is thus an object of the present invention to provide an improved aluminum alloy that can be employed for scroll machine components.
It is a further object of the present invention to provide an improved aluminum alloy that exhibits relatively quick machining times as compared with prior aluminum alloys.
It is a further object of the present invention to provide an aluminum alloy for scroll machine components that exhibits improved wear characteristics as compared with other aluminum alloys.
It is a further object of the present invention to provide an improved aluminum alloy for scroll machine components that obviates the need for sleeve bearings, protective coatings, tip seals, or wear plates between contacting surfaces of other aluminum alloy scroll machine components or of cast iron scroll machine components.
These objects and other advantages are believed obtainable by the subject matter of the present invention, which generally involves the use of an aluminum alloy as a scroll machine component material. In one preferred embodiment, the aluminum alloy employs graphite, which is selectively located at predetermined locations within a scroll machine component. In another preferred embodiment, either with or without graphite in combination with a graphite wetting agent (e.g., nickel coated graphite), the aluminum alloy also incorporates a ceramic reinforcement, preferably aluminum oxide. Other ceramic materials, such as silicon carbide, may optionally be employed.
In yet another preferred embodiment, the graphite and/or ceramic reinforcement are evenly distributed throughout the scroll machine component.